<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

</body>
</html>
<script type="text/javascript">
    'use strict';

    let obj = {y:2};
    console.log(obj.x); // undefined

    let {x,y} = {y:2};
    console.log(x, y); // undefined 2

    let {m:n} = {} // m是undefined，n也是undefined
    console.log(n);

    let {p:k=4} = {}; // 变量k的默认值为4，当p的值为undefined时，k取默认值4
</script>